More precisely, the invention relates to a data transmission electric wire made up of a plurality of conductor strands covered in at least one insulating covering.
Such known wires for the aviation industry comprise conductor strands made of a copper alloy together with an insulating covering comprising an inner tape of polyimide and an outer tape of polytetrafluoroethylene (PTFE). The use of a layer of PTFE serves in particular to improve the ability of the insulating wire to withstand electric arc propagation. The use of a layer of polyimide serves in particular to provide mechanical strength to the insulating covering the cable.
In specific applications such as wires and cables for the aviation and space industries, wires of this type need to be designed so as to present small weight and volume. It is therefore desired to make such an electric wire with a section of about 0.2 square millimeters (mm2) to 0.4 mm2.
For reasons of safety, it is also important for the insulating covering of the wire to present high levels of resistance to cutting and to abrasion, whether by scraping or between wires.
Ordinary polyimides (e.g. sold under the trademarks Kapton® or Apical®, of the 616 type and having a thickness of 30 micrometers (μm)) present high levels of mechanical performance, so an insulating covering that includes them presents relatively high levels of resistance to cutting and to abrasion. In particular, they have been used for more than 30 years in structures with polyimide insulation that do not include PTFE tape (see Table 1, reference CF24), but such structures do not withstand electric arc propagation.
The use of such polyimide 616 tapes in a wire having a core section of 0.2 mm2 with an insulating covering combining polyimide and PTFE, presenting a diameter and a weight that can be close of the structure having the reference CF24, makes it possible to obtain satisfactory resistance to arc propagation, but does not make it possible to obtain insulation with satisfactory resistance to cutting and to abrasion (cf. Table 1, ref. DR24-616). In order to make a wire having a section of 0.2 mm2 and of diameter and weight close to those of the structure referenced CF24, that can withstand electric arc propagation, and that presents insulation with acceptable mechanical properties, it is the practice to use polyimide tapes of smaller thickness, of the order of 22 μm, and of cost and mechanical strength that are higher than those of the 616 tape (trademarks Oasis® or Apical®, and of type 171). Such wires (cf. Table 1, ref. DR24-171) advantageously take the place on aircraft of wires that do not withstand electric arc propagation and that are referenced CF24.
In order to further increase mechanical performance, it can be envisaged to make use of a polyimide of a new generation, that presents better mechanical performance, however such a polyimide is much more expensive than tapes of polyimide 616 or 171, thereby leading to an electric wire that is much too expensive (cf. Table 1, ref. DR24-161).